Kinematic sensors employing atom interferometer phases

ABSTRACT

An apparatus and method for determining the coordinates of a body, where the coordinates express the body&#39;s inertial or kinematic properties, including, for example, its trajectory. The apparatus and method employ atom interferometers provided in a body frame X of the body whose inertial or kinematic properties are to be studied. During operation, interfering entities used by the atom interferometers are released into a known frame X′, such as an inertial frame or the Earth frame X e , that is decoupled from the body frame X and an optical pulse sequence is applied to the interfering entities to affect the quantum-mechanical matter-wave phases of the interfering entities as a function of the coordinates. Under these conditions, the coordinates of the body are determined from the phases of the atom interferometers and analytic expressions for the trajectories of the interfering entities under the simultaneous action of the gravity gradient, Coriolis and centrifugal forces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from provisional U.S. patentapplication No. 60/649,302 filed on Feb. 1, 2005 and herein incorporatedin its entirety.

GOVERNMENT SPONSORSHIP

This application was supported under grant number W911NF-04-1-0047awarded by DARPA, thereby affording the government certain rights inthis invention.

FIELD OF THE INVENTION

The present invention relates generally to kinematic navigationemploying the quantum effect of atom interference and more particularlythe invention allows to navigate by directly using the atominterferometer's phases and without using any accelerometers orgyroscopes.

BACKGROUND OF THE INVENTION

For the purposes of the present invention atom interferometry refersgenerally to quantum mechanical interference processes that involveentities having a rest mass. Among other, such entities include atoms,ions and molecules. For a general overview of the quantum mechanicalprocess of matter-wave interferometry the reader is referred to U.S.Pat. No. 3,761,721 to Altshuler and Franz. For a review of howmatter-wave interferometry is applied in constructing inertial sensorsthe reader is further referred to U.S. Pat. Nos. 4,874,942 and 4,992,656to John F. Clauser and the references cited therein.

Applications of atom interferometry in measuring kinematic properties ofthe various entities such as their velocities and accelerations havebeen explored in more detail by Chu et al. in U.S. Pat. Nos. 5,274,231and 5,274,232. These references teach the use of the Raman process toinduce internal energy transitions and thus affect the internal energystate of the entity as well as other kinematic properties such as itsmomentum or velocity. More precisely, pulses of electromagnetic energyare applied to the entity to stimulate transitions between non-radiativeenergy levels. The detuning of the electromagnetic pulses, i.e., thedifference between the energy levels of the transition and the energyimparted by the electromagnetic pulses allows one to control thedistribution of velocities among the entities. Precise control of thevelocity distribution permits high accuracy measurements of propertiessuch as velocities and accelerations. In turn, such precise measurementsallow one to build more accurate kinematic sensors such asaccelerometers and gyroscopes.

For practical inertial or kinematic navigation the kinematic properties,e.g., accelerations and rotation frequencies of the traveling objectneed not only be measured accurately but also frequently. In fact, formost navigation purposes the kinematic properties of the moving objectsshould be measured at time intervals on the order of 1 ms.Unfortunately, the best measurement accuracy in atom interferometers isobtained when measurements are performed over time intervals rangingfrom 10 ms to 500 ms since the accuracy of an atom interferometricmeasurement increases with measurement time. Hence, prior art atominterferometric sensors designed to serve as accelerometers orgyroscopes are not sufficiently quick for applications in precisekinematic navigation.

OBJECTS AND ADVANTAGES

In view of the above shortcomings of the prior art, the presentinvention has as its objective to provide a method and an apparatus thatpermit direct use of atom interferometric phases, measured in timeintervals optimal for the atom interferometry, for inertial or kinematicnavigation without measuring kinematic properties either at those timesor in between of them.

It is another object of the invention, to provide a method and apparatusthat can measure body trajectory with accuracy on the order of 5 m/hr orbetter, such that it can be used in terrestrial vehicle navigation.

Still other objects and advantages will become apparent from the ensuingdescription.

SUMMARY OF THE INVENTION

The object and advantages of the invention are addressed by a method fordetermining the coordinates of a body, where the coordinates express thebody's inertial or kinematic properties, including, for example, itstrajectory. In accordance with the method, atom interferometers areprovided in a body frame X of the body whose inertial or kinematicproperties are to be studied. During operation, interfering entitiesused by the atom interferometers are released into a known frame X′ thatis decoupled from the body frame X. An optical pulse sequence is thenapplied to the interfering entities to affect the quantum-mechanicalmatter-wave phases of the interfering entities as a function of thecoordinates. Under these conditions, the coordinates of the body aredetermined from the phases of the atom interferometers. The opticalpulse sequence can comprise a π/2-π-π/2 sequence or some other sequence.The pulse sequence can also be a Raman pulse sequence.

In a preferred embodiment the atom interferometers are triggered atregular time intervals. The interfering entities do not necessarily haveto be atoms, and may include any objects exhibiting quantum-mechanicalmatter-wave interference properties. Thus, in general, the interferingentities may consist of atoms, ions and molecules and clusters. In caseof using atoms, it is preferable to release them into the known frame X′in the form of a gas cloud.

In one specific embodiment, the atom interferometers include basic atominterferometers for operating on interfering entities released at aninitial time t_(o) and a zero initial velocity v_(o)=0 in the body frameX. There are preferably three such basic atom interferometers alignedwith three orthogonal axes, e.g., the three axes of a Cartesiancoordinate system. Additional atom interferometers are provided foroperating on interfering entities released at the initial time t_(o) andat a non-zero initial velocity v_(o)≠0 in the body frame X. Whenequipped with basic and additional atom interferometers in this manner,the body rotation matrices R can be determined from phase differencesbetween the basic and the additional atom interferometers and fromrotation matrices R restored for preceding measurement times. Bodycoordinates can also be determined from the phases of the basic atominterferometers, restored rotation matrices R, and body coordinatesrestored from preceding measurement times and body velocities at thetimes of releasing the interfering entities.

In some embodiments of the method, the velocity of the body at the timeof releasing the interfering entities for subsequent atominterferometric measurements is obtained by interpolation from restoredbody positions. Depending on the specific implementation of the method,the velocity of the body can be measured at predetermined body positionsor the velocity of the body can be excluded.

In terrestrial applications, the method is practiced in situations wherethe known frame X′ is the Earth frame X_(e). For reasons of accuracy, itis important that in these applications the initial velocity of theinterfering entities released at initial time t_(o) in the Earth frameX_(e) be sufficiently small to allow the Earth's gravity potential V(r)to be expressed by the following expression:V({right arrow over (r)})=V _(o) −{right arrow over (x)}·{right arrowover (g)} _(e) −T _(ik) x _(i) x _(k),where g_(e) is gravity acceleration and T_(ik) is gravity gradienttensor. Also, especially when tracking the trajectory of the body overlonger distances, it is advantageous that the Earth's gravity potentialinclude both a normal gravity potential V^((n)) (r) and an anomalousgravity potential V^((a)) (r).

The invention further extends to an apparatus for determining thecoordinates of the body. The apparatus has atom interferometers that aremounted in the body frame X, e.g., by being firmly attached to the bodyat a convenient location. The atom interferometers use interferingentities that are released into the known frame X′ which is decoupledfrom the body frame X. Furthermore, the apparatus has a source forapplying an optical pulse sequence to the interfering entities andthereby affect the matter-wave phases of the interfering entities as afunction of the coordinates. The apparatus has a unit that determinesthe coordinates of the body from the phases of the atom interferometers.

The apparatus can use basic atom interferometers and additional atominterferometers for operating on interfering entities released at zeroand non-zero initial velocities v_(o) in body frame X. The interferingentities can be atoms, ions, molecules or clusters.

The apparatus can be employed in any body, for example a vehicle, thatmoves on the surface of the Earth, in the Earth's atmosphere, in outerspace or indeed any environment that is inertial or non-inertial. Inmany applications, the vehicle will be earth-bound and therefore beconfined to trajectories in the Earth frame.

The specific embodiments of the apparatus and particular applications ofthe method are described in the below detailed description withreference to the drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a three-dimensional diagram illustrating the basic principlesof the apparatus and method of the invention.

FIG. 2 is a diagram illustrating some operational details of thequantum-mechanical matter-wave interference mechanism employed by theinvention.

FIG. 3 is a diagram illustrating how Euler angles can be used inrotation matrices R.

FIG. 4 is a diagram illustrating the method of invention in the casewhere the known frame is an inertial frame and the body undergoes norotation.

FIG. 5 is a diagram illustrating the use of three interferometers torecover body trajectory in the case shown in FIG. 4.

FIG. 6 is a three-dimensional diagram showing a way of practicing themethod when the known frame X′ is a homogeneous gravity frame and thebody rotates.

FIG. 7 is a three-dimensional diagram showing a way of practicing themethod when the known frame X′ is the Earth frame X_(e).

FIG. 8 is a graph of the time dependence of the error in rotation matrixrestoration for different levels of error in interferometer phases δφ.

FIG. 9A-E are graphs illustrating the maximum time for body motionrestoration and optimum number of interpolation points as a function oftime delay between pulses for oscillatory body motion.

FIG. 10 are graphs of initial and final portions of body motion, exactand restored using atom interferometer phases and interpolation inaccordance with the invention for oscillatory body motion.

FIG. 11A-E are graphs illustrating the maximum time for body motionrestoration and optimum number of interpolation points as a function oftime delay between pulses for pulsed body motion.

FIG. 12A-E are graphs of initial and final portions of body motion,exact and restored using atom interferometer phases and interpolation inaccordance with the invention for pulsed body motion.

FIG. 13 are graphs for simulations of five different trajectories of abody moving the Earth frame illustrating the dependence of the maximumnavigation time on the time delay T between Raman pulses.

FIG. 14 are graphs for the simulations of FIG. 13 showing the build upof error in body position, body velocity and gravity acceleration duringthe navigation process.

DETAILED DESCRIPTION

FIG. 1 illustrates a body 10 whose coordinates are to be determined. Inthe example shown, body 10 is a vehicle, and in particular a plane. Itshould be noted that body 10 can be any vehicle in the broadest sense ofthe term or indeed any object whose coordinates or motion is to bedetermined. In some cases, body refers to a navigation platform, as willbe clear to person's skilled in the art. Body 10 may be earth-bound tomove in the Earth's atmosphere, on its surface, in outer space or indeedin any inertial or non-inertial frame that is known and will be referredto as known frame X′.

Vehicle 10 has a unit 12 that houses a number of atom interferometers14. Atom interferometers 14 are fixed in the non-inertial referenceframe or body frame X of vehicle 10. In the present case, body frame Xof vehicle 10 is described in Cartesian coordinates x₁, x₂, x₃. It willbe understood by those skilled in the art, that depending on thesymmetry and the trajectory of body 10 a different coordinate system,e.g., a spherical coordinate system can be employed.

At an initial time t_(o) interfering entities 16 are released into theknown frame X′ that is decoupled from body frame X. The frame into whichentities 16 are released can be an inertial or non-inertial frame X′. Inouter space virtually no gravitational force acts on entities 16 andthus known frame X′ is an inertial frame in which the motion of entities16 is rectilinear. It should be noted that interfering entities 16 canbe atoms, ions, molecules or any entities of matter that will undergoquantum-mechanical matter-wave interference capable of atominterferometric measurement.

In the present case, entities 16 are released near the Earth 18. Hence,known frame X′ is the Earth frame and it is described in Cartesiancoordinates x′₁, x′₂, x′₃. The Earth's gravitational field g and theEarth's rotation Ω determine the forces acting on entities 16 in Earthframe X′. In fact, once released into Earth frame X′ entities 16 followan inertial trajectory 20 that is governed by gravitational, Coriolisand centrifugal forces as well as gravity-gradient induced forces.

In the present embodiment, interfering entities 16 are atoms that form agas cloud 17. Atoms 16 are released at an initial velocity v_(o) asmeasured in body frame X. Initial velocity v_(o) can be zero ornon-zero. Note that boldface as well as superscripted arrows are used todenote vector quantities throughout the document.

In a preferred embodiment, atoms 16 are released at both a zero initialvelocity v_(o)=0 and a non-zero initial velocity v_(o)≠0 such thatinterferometeric measurements can be performed by atom interferometers14 on entities 16 with different initial velocities v_(o) to help inrecovering the coordinates in accordance with a preferred method.Although only two atom interferometers 14 having optical pulsespropagating along axes x₁ and x₂ are shown in FIG. 1, it is understoodthat more can be used.

Over time, vehicle 10 executes a body motion that is described by atrajectory 22. In addition to following trajectory 22, vehicle 10 alsochanges its orientation or undergoes rotation as expressed by a rotationmatrix R. The trajectory of vehicle 10 can be described by its positionin time, or X(t). It is an objective of the method and apparatus of theinvention to keep the error ΔX of this navigation method to less than 5m over the course of one hour or:ΔX<5 m.  Eq. 1

Note that unit 12 is indicated in a dashed line and gas cloud 17 of gasatoms 16 is shown following inertial trajectory 20 that extends outsidevehicle 10. This is done for illustrative purposes to clearly show howgas atoms 16 once released into Earth frame X′ follow inertialtrajectory 20 instead of the non-inertial trajectory 22 and rotationenforced on plane 10 by its propulsion system and aerodynamic forces. Inpractice, the method of invention is performed on short time scales suchthat entities 16 do not travel outside a small unit 12 during themeasurement.

Specifically, after release of atoms 16 at initial time t_(o) an opticalpulse sequence 24 is applied to them at times t_(o)+t₁, t_(o)+t₁+T,t_(o)+t₁+2T, where t₁ is a possible time delay between the release orlaunching times of atoms 16 and the application of the first opticalpulse and T is the time separation between the pulses of the sequence.In this particular case sequence 24 is a Raman pulse sequence and X₁,R₁; X₂, R₂; X₃, R₃ correspond to the coordinates and the rotationmatrices R of body frame X at times t_(o)+t₁, t_(o)+t₁+T, t_(o)+t₁+2T.The Euler angle convention used in rotation matrices R that quantify therotation of body frame X is illustrated in FIG. 3. For a more thoroughtreatment of Euler angles and rotation conventions the reader isreferred to Chapter 4 of Goldstein et al., Classical Mechanics, 3^(rd)Edition, Addison Wesley 2002.

Pulse sequence 24 is preferably a π/2-π-π/2 sequence of Raman pulsesspaced at equal time intervals T. In other words, the Raman pulses occurwith time delay T after an initial time t_(o)=0 at which entities 16 arereleased into Earth frame X_(e) and at discrete subsequent times thatcan be described as t=jT, where j=0, 1, 2. Before considering thecomplete description of the motion of entities 16 after their releaseinto Earth frame X_(e) it is useful to first review the basic principlesof operation of atom interferometers 14.

In the diagram of FIG. 2 only one gas atom 16 is shown in one of atominterferometers 14, namely atom interferometer 14A. Atom 16 can be in alow energy state |lo> or a high energy state |hi>. Note that low |lo>and high |hi> energy states as used herein are purposely general, butgiven specific atoms 16 respective specific energy states of those atoms16 will be used. The wavelengths of the radiation in optical pulses 24are selected to operate on a transition between low |lo> and high |hi>energy states and thus separate the matter-waves associated with atom16. Once separated, the matter-waves associated with low |lo> and high|hi> energy states follow inertial trajectory 20 along slightlydifferent paths. In particular, matter-waves associated with low energystate |lo> follow a path 20A and matter-waves associated with highenergy state |hi> follow a path 20B.

The splitting of inertial trajectory 20 into paths 20A, 20B anddifferent evolution of matter-waves propagating along paths 20A, 20Bgives rise to the quantum interference effect used in this invention.The phases of the matter-waves undergo different amounts of changedepending on their path as well as applied optical pulse sequence 24.Since body frame X in which optical pulse sequence 24 is generated movesalong with body 10 relative to paths 20A, 20B the coordinates of body 10affect the optical pulses sequence 24 that acts on the matter-wavespropagating along paths 20A, 20B. More precisely, optical pulse sequence24 affects matter-wave phases of interfering entities 16 as a functionof the coordinates of body 10.

The application of optical pulse sequence 24 affects the phases of thetwo interfering matter-wave packets on paths 20A, 20B and yieldsdifferent measurement results at outputs 26, 28 of interferometer 14A.In other words, different numbers of atoms 16 are measured at output 26in high energy state |hi> and at output 28 in low energy state |lo> as afunction of position and rotation of body frame X. The coordinates androtation matrices acting on body frame X, or equivalently on body 10,are determined by a unit 30 from the phases of a number ofinterferometers 14.

Additional information about the use of Raman pulse sequences for atominterferometric measurements on entities in the inertial frame ofreference is contained in Kai Bongs, et al., “High-order inertial phaseshifts for time-domain atom interferometers”, Physics Department, YaleUniversity, 25 Feb. 2003 published on the web athttp://xxx.lanl.gov/abs/quant-ph/0204102, which is herein incorporatedby reference. It should be noted that any suitable type of opticalexcitation method may be used, including single photon, two photon(Raman) and multi-photon (3 photon and higher) excitations.

Operation Without Body Rotation and in the Absence of Gravity

To best understand the method of invention in detail, it is instructiveto first consider the simplest case in which vehicle 10 is moving in anenvironment without gravity and undergoes no rotation, as shown in thediagram of FIG. 4. In other words, known frame X′ is an inertial frame,and body frame X follows a trajectory 22 but does not rotate. Wheninterfering entities 16 are released as a gas cloud 17 into inertialframe X′ at initial time t_(o), the initial velocity v_(o) at whichentities 16 are released in body frame X does not change with time. Thismeans that trajectory 20 of entities 16 follows a straight line ininertial frame X′; i.e., trajectory 20 is rectilinear. In someembodiments initial velocity v_(o) in body frame X is zero and in someother embodiments it is non-zero, depending on application and as willbe discussed below.

Pulse sequence 24 is a π/2-π-π/2 sequence of Raman pulses spaced atequal time intervals T. In other words, the Raman pulses occur with timedelay T after an initial time t_(o)=0 at which entities 16 are releasedinto inertial frame X′ and at discrete subsequent times T and 2T. Underthese conditions, the interference between the different atomic passeshas a phase φ given by:φ={right arrow over (k)}[{right arrow over (x)}(t _(o))−2{right arrowover (x)}(t _(o) +T)+{right arrow over (x)}(t _(o)+2T)],  Eq. 2where k is an effective wave vector associated with the Raman process,{right arrow over (x)}(t)={right arrow over (x)}′(t)−{right arrow over(X)}(t)  Eq. 3

x(t) and x′(t) are positions of the center of cloud 17 in noninertialbody frame X and inertial frame X′. Since in inertial frame X′ entities16 move with constant velocity v′, trajectory 20 is described by:{right arrow over (x)}′(t)={right arrow over (x)}′(t _(o))+{right arrowover (v)}′(t−t _(o)),  Eq. 4and thus, in body frame X one finds:{right arrow over (x)}(t)={right arrow over (x)}(t _(o))+{right arrowover (X)}(t _(o))−{right arrow over (X)}(t)+{right arrow over (v)}′(t−t_(o)).  Eq. 5

Substituting equation 5 into equation 2, we can see that in the absenceof rotation, interferometer phase is velocity insensitive and can beexpressed in body frame X by:φ=−{right arrow over (k)}[{right arrow over (X)}(t _(o))−2{right arrowover (X)}(t _(o) +T)+{right arrow over (X)}(t _(o)+2T)].  Eq. 6

Since the interferometers are launched when entities 16 are released attimes t_(o)=jT, and the corresponding phases φ_(j) are measured, one canexpress X_(j+2) through X_(j+1) and X_(j) and restore step by steptrajectory 22 of vehicle 10 at these times when X_(o) and X₁ are known.To accomplish this, we rewrite equation 6 as:δX _(j) =δX _(j−1)−φ_(j−2) , j≧2,  Eq. 7where δX_(j)=X_(j)−X_(j−1), X_(j)={right arrow over (k)}·{right arrowover (X)}_(j), and find its solution,${\delta\quad X_{j}} = {{\delta\quad X_{1}} - {\sum\limits_{j^{\prime} = 0}^{j - 2}\quad\phi_{j^{\prime},}}}$from which$X_{j} = {X_{o} + {{j\delta}\quad X_{1}} - {\sum\limits_{j^{\prime} = 2}^{j}\quad{\sum\limits_{j^{''} = 0}^{j^{\prime} - 2}\quad\phi_{j^{''}.}}}}$Changing the order of summation we obtain the expression:$\begin{matrix}{{X_{j} = {X_{o} + {{j\delta}\quad X_{1}} - {\sum\limits_{j^{\prime} = 0}^{j - 2}{\left( {j - j^{\prime} - 1} \right)\phi_{j^{\prime}}}}}};{j \geq 2.}} & {{Eq}.\quad 8}\end{matrix}$

In cases where vehicle 10 acceleration is constant, we know thatφ_(j)=−{right arrow over (k)}·{right arrow over (a)}T². In this case,since${{\overset{->}{X}}_{1} = {{\overset{->}{X}}_{o} + {{\overset{->}{V}}_{o}T} + \frac{\overset{->}{a}T^{2}}{2}}},$where V_(o) is the platform/body velocity—equation 8 reduces to thesimple expression: $\begin{matrix}{X_{j} = {{\overset{->}{k}\left\lbrack {\overset{->}{X_{o}} + {{\overset{->}{V}}_{o}{jT}} + \frac{\overset{->}{a}j^{2}T^{2}}{2}} \right\rbrack}.}} & {{Eq}.\quad 9}\end{matrix}$

We thus see that three interferometers 14A, 14B and 14C having mutuallyperpendicular wave vectors k₁, k₂, and k₃ as shown in FIG. 5, aresufficient to restore trajectory 22 of vehicle 10 without measuring bodyacceleration and velocity if the positions of vehicle 10 at moments X(0)and X(T) are premeasured independently.

Operation Including Body Rotation in an Inertial Frame with aHomogeneous Gravity Field

FIG. 6 illustrates an application where vehicle 10 undergoes rotationduring its motion in a known frame X′ that is inertial. The rotation isdescribed by rotation matrix R(t). When one calculates interferometers'phases in the inertial frame, R(t) (just like vehicle position X(t) inthe case of FIG. 4) has to be treated as an unknown matrix which has tobe restored from the values of the phases.

Although the rotation between phase measurements can be significant, wecan assume for simplicity of explanation, that rotation is small duringthe corresponding motion of vehicle 10. In other words, the rotationmatrix can be expressed by: $\begin{matrix}{{{R(t)} \approx \begin{pmatrix}1 & {\psi_{3}(t)} & {- {\psi_{2}(t)}} \\{- {\psi_{3}(t)}} & 1 & {\psi_{1}(t)} \\{\psi_{2}(t)} & {- {\psi_{1}(t)}} & 1\end{pmatrix}},{where}} & {{Eq}.\quad 10} \\{{{\overset{->}{\psi}(t)} = {\int_{0}^{t}\quad{{\mathbb{d}t^{\prime}}{\overset{->}{\Omega}\left( t^{\prime} \right)}}}},} & {{Eq}.\quad 11}\end{matrix}$and Ω(t) is the rotation frequency.

The trajectory 20 of cloud 17 of entities 16, in this case atoms, ininertial frame X′ is still given by equation 4. Meanwhile, in thenoninertial body frame X the motion of cloud 17 is described by:{right arrow over (x)}(t)=[1−{right arrow over (ψ)}(t)×][{right arrowover (x)}′(t)−{right arrow over (X)}′(t)].  Eq. 12

Assuming for simplicity that cloud 17 is launched in the center of thenoninertial body frame X, as shown in FIG. 6, we obtain from equation 12v′={right arrow over (V)}+[1+{right arrow over (ψ)}(t_(o))×]{right arrowover (v)}_(o) (where V and v_(o) are respectively the initial (att=t_(o)) velocity of vehicle 10 and velocity of cloud 17 in body frameX), and therefore:{right arrow over (x)}(t)=[1−{right arrow over (ψ)}(t)×][{right arrowover (X)}(t _(o))−{right arrow over (X)}(t)+(t−t _(o)){right arrow over(V)}]+(t−t _(o)){1+[{right arrow over (ψ)}(t _(o))−{right arrow over(ψ)}(t)]×}{right arrow over (v)} _(o).  Eq. 13

Since unknown rotation angles ψ(t) and position X(t) are coupled inequation 13, three interferometers 14A, 14B, and 14C (see FIG. 5) havingmutually perpendicular wave vectors as used in the previous embodimentare not sufficient to determine the six unknowns. As a result, threeadditional interferometers 14D, 14E, and 14F have to be used inconjunction with interferometers 14A, 14B, and 14C. To be sensitive tothe same rotation matrices and positions all interferometers 14 have tobe synchronized.

In the present embodiment, entities 16 for interferometric measurementby the first three interferometers 14A, 14B, and 14C, referred to asbasic interferometers (BI) are launched or released into inertial frameX′ at zero initial velocity v=0. In addition, entities 16 forinterferometric measurement with interferometers 14D, 14E, and 14F,referred to as additional interferometers (AI) are launched or releasedinto inertial frame X′ at a non-zero initial velocity v≠0. Also,delaying optical pulse sequence 24 of Raman pulses to affect matter-wavephases of interfering entities 16 to time t₁ after initial time to isbeneficial to the method. Pulse sequence 24 is thus a π/2-π-π/2 sequenceof Raman pulses spaced at equal time intervals T commencing at timet_(o)+t₁ and at discrete subsequent times t_(o)+t₁+T and t_(o)+t₁+2T.Under these conditions, we can express the phase through X(t) and ψ(t)as: $\begin{matrix}{{{\phi\left( {t_{o},t_{1},\overset{->}{v}} \right)} = {\overset{->}{k} \cdot {\overset{->}{\chi}\left( {t_{o},t_{1},\overset{->}{v}} \right)}}};\quad{where}} & {{{Eq}.\quad 14}a} \\{{{\overset{->}{\chi}\left( {t_{o},t_{1},\overset{->}{v}} \right)} \equiv {{\overset{->}{x}\left( {t_{o} + t_{1} + {2T}} \right)} - {2{\overset{->}{x}\left( {t_{o} + t_{1} + T} \right)}} + {\overset{->}{x}\left( {t_{o} + t_{1}} \right)}}} = {{2\left\lbrack {1 - {{\overset{->}{\psi}\left( {t_{o} + t_{1} + T} \right)} \times}} \right\rbrack}{\quad{\left\lbrack {{\overset{->}{X}\left( {t_{o} + t_{1} + T} \right)} - {\overset{->}{X}\left( t_{o} \right)}} \right\rbrack - {\left\lbrack {1 - {{\overset{->}{\psi}\left( {t_{o} + t_{1} + {2T}} \right)} \times}} \right\rbrack\left\lbrack {{\overset{->}{X}\left( {t_{o} + t_{1} + {2T}} \right)} - {\overset{->}{X}\left( t_{o} \right)}} \right\rbrack} - {\left\lbrack {1 - {{\overset{->}{\psi}\left( {t_{o} + t_{1}} \right)} \times}} \right\rbrack\left\lbrack {{\overset{->}{X}\left( {t_{o} + t_{1}} \right)} - {\overset{->}{X}\left( t_{o} \right)}} \right\rbrack} +}}}} & {{{Eq}.\quad 14}b} \\{\left\lbrack {{2\left( {t_{1} + T} \right){\overset{->}{\psi}\left( {t_{o} + t_{1} + T} \right)}} - {\left( {t_{1} + {2T}} \right){\overset{->}{\psi}\left( {t_{o} + t_{1} + {2T}} \right)}} - {t_{1}{\overset{->}{\psi}\left( {t_{o} + t_{1}} \right)}}} \right\rbrack \times {\left( {\overset{->}{V} + \overset{->}{v}} \right).}} & {{{Eq}.\quad 14}c}\end{matrix}$

For a given wave vector k the phase difference between AI and BI issensitive only to the rotation angles ψ, $\begin{matrix}{{\phi_{r} \equiv {{\phi\left( {t_{o},t_{1},\overset{->}{v}} \right)} - {\phi\left( {t_{o},t_{1},0} \right)}}} = {\left\lbrack {{\left( {t_{1} + {2T}} \right){\overset{->}{\psi}\left( {t_{o} + t_{1} + {2T}} \right)}} - {2\left( {t_{1} + T} \right){\overset{->}{\psi}\left( {t_{o} + t_{1} + T} \right)}} + {t_{1}{\overset{->}{\psi}\left( {t_{o} + t_{1}} \right)}}} \right\rbrack \cdot \left( {\overset{->}{k} \times \overset{->}{v}} \right)}} & {{Eq}.\quad 15}\end{matrix}$and if angles at preceding times t_(o)+t₁ and t_(o)+t₁+T are alreadyknown, then the vector ψ(t_(o)+t₁+2T) can be restored using phasedifference 15. For example, to get ψ₁(t_(o)+t₁+2T) one needs to use anAI in which atoms are launched along axis 3 and wave vector directedalong axis 2, measure the phase difference between this AI and the BIhaving the same wave vector and get: $\begin{matrix}{{\psi_{1}\left( {t_{o} + t_{1} + {2T}} \right)} = {{\frac{1}{t_{1} + {2T}}\left\lbrack {\frac{\phi_{r}}{kv} + {2\left( {t_{1} + T} \right){\psi_{1}\left( {t_{o} + t_{1} + T} \right)}} - {t_{1}{\psi_{1}\left( {t_{o} + t_{1}} \right)}}} \right\rbrack}.}} & {{Eq}.\quad 16}\end{matrix}$

We see that this approach can be repeated with two additional AIs thathave velocity vectors directed along axes 3 and 1 and wave vectorsdirected along axes 1 and 2, respectively to obtain ψ₂(t_(o)+t₁+2T) andψ₃(t_(o)+t₁+2T) in the same manner.

It is important to underline that rotation angles ψ can be restored stepby step from phase differences φ_(r) only since they are not coupled tovelocity V or position X of vehicle 10. In fact, because of the absenceof such coupling, it is possible to restore the orientation of vehicle10 with much greater accuracy than even its position.

After finding the vector ψ(t), one can turn attention to the BI phasesas follows:φ={right arrow over (k)}·{right arrow over (χ)}(t _(o) ,t _(i),0); where  Eq. 17a{right arrow over (χ)}(t _(o) ,t ₁,0)=2[1−{right arrow over (ψ)}(t _(o)+t ₁ +T)×][{right arrow over (X)}(t _(o) +t ₁ +T)−{right arrow over(X)}(t _(o))]−[1−{right arrow over (ψ)}(t _(o) +t ₁+2T)×][{right arrowover (X)}( t _(o) +t ₁+2T)−{right arrow over (X)}(t _(o))]−[1−{rightarrow over (ψ)}(t _(o) +t ₁)×][{right arrow over (X)}(t _(o) +t₁)−{right arrow over (X)}(t _(o))]+[2(t ₁ T){right arrow over (ψ)}(t_(o) +t ₁ +T)−(t ₁+2T){right arrow over (ψ)}( t _(o) +t ₁+2T)−t ₁{rightarrow over (ψ)}(r _(o) +t ₁)]×{right arrow over (V)}.  Eq. 17b

Note that at this point, since we have restored the orientation, theonly unknown is body velocity vector V at the initial time t_(o) whenentities 16 were released. There are a number of techniques that can beused to obtain vector V.

The first technique is based on interpolation that employs atominterferometric measurements, which normally cannot be used for thispurpose. In accordance with the invention, however, atom interferometricmeasurements are used to recover V by introducing a time delay betweeninitial time to at which entities 16 are released and the time whenfirst Raman pulse is applied, namely t_(o)+t₁, as shown in FIG. 6. Inone particular embodiment of this method, initial time t_(o)=0, V=0 anda number 6(n_(i)−2) interferometers launched at the times:$\begin{matrix}\begin{matrix}{{interferometers}\quad 1\ldots\quad 6} & {t_{1} = 0} & T & {2T} & \quad & \quad \\{{interferometers}\quad 7\ldots\quad 12} & \quad & {t_{1} = T} & {2T} & {3T} & \quad \\\vdots & \vdots & \vdots & \vdots & {\quad\vdots} & \quad \\{{{interferometers}\quad 6\left( {n_{i} - 3} \right)} + {1\ldots\quad 6\left( {n_{i} - 2} \right)}} & \quad & \quad & \quad & \cdots & {{t_{1} = {\left( {n_{i} - 3} \right)T}},{\left( {n_{i} - 2} \right)T},{\left( {n_{i} - 1} \right)T}}\end{matrix} & {{Eq}.\quad 18}\end{matrix}$

Here we assume that both position X of vehicle 10 and rotation matrix Rat times 0 and T are known. In this case the rotation angles ψ₁, ψ₂ andψ₃ can be obtained by applying equation 16 as shown above. Since allclouds 17 are launched at the same time, namely at initial time t_(o),the vehicle velocity vector V=0 for all of them. Now, by resolvingequation 17b with respect to X(t_(o)+t₁+2T) one restores body positionsat all n_(i) points t=0, . . . (n_(i)−1)T.

Since the last adjacent pair of times are (n_(i)−2)T and (n_(i)−1)T, thelatest times when the next set of 6(n_(i)−2) interferometers should belaunched is t_(o)=(n_(i)−2)T, but in this case one needs to find bodyvelocity V. For this purpose we fit trajectory 22 of vehicle 10 by aninterpolation polynomial. For example, for n_(i)=3 one can use a linearfit: $\begin{matrix}{{\overset{->}{V} \approx \frac{{\overset{->}{X}\left\lbrack {2T} \right\rbrack} - {\overset{->}{X}\lbrack 0\rbrack}}{2T}},} & {{Eq}.\quad 19}\end{matrix}$while for larger number of interpolation points n_(i), we use a thirdorder interpolation polynomial, for which one finds: $\begin{matrix}{\overset{->}{V} \approx {\frac{1}{6T}{\left\{ {{2{\overset{->}{X}\left\lbrack {\left( {n_{i} - 1} \right)T} \right\rbrack}} + {3{\overset{->}{X}\left\lbrack {\left( {n_{i} - 2} \right)T} \right\rbrack}} - {6{\overset{->}{X}\left\lbrack {\left( {n_{i} - 3} \right)T} \right\rbrack}} + {\overset{->}{X}\left\lbrack {\left( {n_{i} - 4} \right)T} \right\rbrack}} \right\}.}}} & {{Eq}.\quad 20}\end{matrix}$Using this approach one finds positions X for the next n_(i)−2 pointsreaching time (2n_(i)−3)T and then repeats the process.

Another technique to obtain vector V can measure it directly by using3×6 interferometers. In still another approach one can simply exclude V.This may be used when the time delays between the optical pulses is amultiple of T.

Operation Including Body Rotation in the Earth Frame

FIG. 7 illustrates an embodiment designed for terrestrial applications,i.e., situations where the interferometric method is practiced oninterfering entities 16 released into the Earth frame X′. For reasons ofclarity, Earth frame X′ is specifically referred to as X_(e) in FIG. 7,and the subscript “e” is used in the below equations to denote vectorsand quantities expressed in the Earth frame. We will also separatelynumber the equations in this section in order to make the method easierto follow.

We once again require that:ΔX<5 m,  Eq. 1and that the time during which this inequality is to be obeyed is:t≦1 hr.  Eq. 2

For simplicity, vehicle 10 and atom interferometers 14 are not shown inthis drawing and only unit 12 is indicated. We consider navigation ofvehicle 10 moving in the normal gravity field V^((n))(r) of rotatingEarth 18, where the gravity potential is given by: $\begin{matrix}{{{V^{(n)}\left( \overset{->}{r} \right)} = {{- \frac{GM}{r}}\left( {1 - {\sum\limits_{m = 1}^{\infty}{{J_{2m}\left( \frac{a_{E}}{r} \right)}^{2m}{P_{2m}\left( {\cos\quad\theta} \right)}}}} \right)}},} & {{{Eq}.\quad 3}a} \\{{J_{2m} = {\left( {- 1} \right)^{m + 1}\frac{3{\mathbb{e}}^{2m}}{\left( {{2m} + 1} \right)\left( {{2m} + 3} \right)}\left( {1 - {m\left( {1 - \frac{5J_{2}}{{\mathbb{e}}^{2}}} \right)}} \right)}},} & {{{Eq}.\quad 3}b}\end{matrix}$where θ is the angle between vector r and the North direction (z-axis),P₂₁(cos θ) is the Legendre polynomial, GM=3.986004415·10¹⁴ m³s⁻² is thegeocentric gravitational constant, a_(E)=6378136.3 m is the equatorialradius, e²=f(2−f) is the first eccentricity, f is the polar flattening(1/f=298.25765), and J₂=1.0826267·10⁻³ is the dynamic form factor of theEarth. Entities 16 (only one shown in FIG. 4 for reasons of clarity)move in a small vicinity 32 of point X_(e) denoted by the vectorextending to the point at which atom 16 is released from body frame Xinto Earth frame X′. In other words:{right arrow over (r)}={right arrow over (X)}+{right arrow over (x)},where x<<X.  Eq. 4

This constraint is important for accuracy of the method and can beensured with a small initial velocity v_(o) of interfering entities 16in the body frame X and/or sufficiently small velocity V of vehicle 10.

With the constraint of entities 16 moving in small vicinity 32 duringthe atomic interferometric measurement, the normal gravity potential canbe reformulated with the aid of the following expansions:$\begin{matrix}{{{\frac{1}{r^{s}} = {\frac{1}{X^{s}}\left( {1 - \frac{s{\overset{->}{x} \cdot \overset{->}{n}}}{X} - \frac{s\left( {x^{2} - {\left( {s + 2} \right)\left( {\overset{->}{x} \cdot \overset{->}{n}} \right)^{2}}} \right)}{2X^{2}}} \right)}};}{{P_{2m}\left( {\cos\quad\theta} \right)} \approx {{P_{2m}\left( {\cos\quad\Theta} \right)} + {{P_{2m}^{\prime}\left( {\cos\quad\Theta} \right)}\frac{\overset{->}{x} \cdot \left( {\overset{->}{z} - {\overset{->}{n}\quad\cos\quad\Theta}} \right)}{X}} - {\frac{1}{2X^{2}}\left\lbrack {{{P_{2m}^{\prime}\left( {\cos\quad\Theta} \right)}\left\lbrack {{\cos\quad{\Theta\left\lbrack {x^{2} - {3\left( {\overset{->}{n} \cdot \overset{->}{x}} \right)^{2}}} \right\rbrack}} + {2\left( {\overset{->}{n} \cdot \overset{->}{x}} \right)\left( {\overset{->}{n} \cdot \overset{->}{x}} \right)}} \right\rbrack} - {2{P_{2m}^{''}\left( {\cos\quad\Theta} \right)}\left( {{\overset{->}{x} \cdot \overset{->}{z}} - {{\overset{->}{x} \cdot \overset{->}{n}}\quad\cos\quad\Theta}} \right)^{2}}} \right\rbrack}}}} & {{Eq}.\quad 6}\end{matrix}$where n=X/X, z is a unit vector in the North direction, and Θ is theangle between vectors n and z, as shown in FIG. 7. Using theseexpansions the Earth's normal gravity potential V(r) to be expressed asfollows:V ^((n))({right arrow over (r)})=V _(o) −{right arrow over (x)}·{rightarrow over (g)} _(e) −T _(ik) x _(i) x _(k),  Eq. 7where g_(e) is the gravity acceleration and T_(ik) is a gravity gradienttensor. These are given by: $\begin{matrix}{{{\overset{->}{g}}_{e} = {g\left( {{a\overset{->}{n}} + {b\overset{->}{z}}} \right)}},{{in}\quad{which}}} & {{{Eq}.\quad 8}a} \\{{g = {- \frac{GM}{X^{2}}}},} & {{{Eq}.\quad 8}b} \\{{a = {1 - {\sum\limits_{m = 1}^{\infty}{J_{2m}\frac{a^{2m}}{\sin^{2}{\Theta X}^{2m}}\left\{ {{\left\lbrack {{2m} + 1 - {\left( {{4m} + 1} \right)\quad\cos^{2}\Theta}} \right\rbrack{P_{2m}\left( {\cos\quad\Theta} \right)}} + {2m\quad\cos\quad\Theta\quad{P_{{2m} - 1}\left( {\cos\quad\Theta} \right)}}} \right\}}}}},} & {{{Eq}.\quad 8}c} \\{{b = {2{\sum\limits_{m = 1}^{\infty}{J_{2m}{\frac{{ma}_{E}^{2m}}{\sin^{2}{\Theta X}^{2m}}\left\lbrack {{P_{{2m} - 1}\left( {\cos\quad\Theta} \right)} - {\cos\quad\Theta\quad{P_{2m}\left( {\cos\quad\Theta} \right)}}} \right\rbrack}}}}},{and}} & {{{Eq}.\quad 8}d} \\{{T_{ik} = {\frac{\tau_{z}}{4}\left\lbrack {{- {a\delta}_{ik}} + {{dn}_{i}n_{k}} + {{ez}_{i}z_{k}} + {\frac{f}{2}\left( {{z_{i}n_{k}} + {z_{k}n_{i}}} \right)}} \right\rbrack}},{{in}\quad{which}}} & {{{Eq}.\quad 8}e} \\{{\tau_{z} = {2\frac{GM}{X^{3}}}},} & {{{Eq}.\quad 8}f} \\{\left. {d = {3 - {\sum\limits_{m = 1}^{\infty}{J_{2m}\frac{a^{2m}}{\sin^{4}{\Theta X}^{2m}} \times \left\{ {\left\lbrack {{\left( {{2m} + 1} \right){\left( {{2m} + 3 - {2\cos^{2}\Theta}} \right)\left\lbrack {3 + {14m} + {10m^{2}}} \right\rbrack}} + {\cos^{4}{\Theta\left( {{4m} + 3} \right)}\left( {{4m} + 1} \right)}} \right\rbrack{P_{2m}\left( {\cos\quad\Theta} \right)}} \right\}}} + {2{m\left\lbrack {{4m} + 5 - {\left( {{4m} + 3} \right)\cos^{2}\Theta}} \right\rbrack}{P_{2m}\left( {\cos\quad\Theta} \right)}} - {2\cos\quad{{\Theta P}_{{2m} - 1}\left( {\cos\quad\Theta} \right)}}}} \right\},} & {{{Eq}.\quad 8}g} \\{{e = {2{\sum\limits_{m = 1}^{\infty}{J_{2m}\frac{{ma}^{2m}}{\sin^{4}{\Theta X}^{2m}}\left\{ {{\left\lbrack {{2m} + 1 - {\left( {{2m} - 1} \right)\cos^{2}\Theta}} \right\rbrack{P_{2m}\left( {\cos\quad\Theta} \right)}} - {2\quad\cos\quad{{\Theta P}_{{2m} - 1}\left( {\cos\quad\Theta} \right)}}} \right\}}}}},} & {{{Eq}.\quad 8}h} \\{f = {{4{\sum\limits_{m = 1}^{\infty}{J_{2m}{\frac{a^{2m}}{\sin^{4}{\Theta X}^{2m}}\left\lbrack \quad{{{- \left\lbrack {{4\quad m}\quad + \quad 3\quad - \quad{\left( {{4\quad m}\quad + \quad 1} \right)\quad\cos^{2}\quad\Theta}} \right\rbrack}\cos\quad{{\theta P}_{2\quad m}\left( {\cos\quad\Theta} \right)}} +} \right\rbrack}}}} + {{{2\left\lbrack {m\quad + \quad 1\quad - \quad{m\quad\cos^{2}\quad\Theta}} \right\rbrack}\left\lbrack \quad{P_{{2\quad m}\quad - \quad 1}\left( {\cos\quad\Theta} \right)} \right\rbrack}.}}} & {{{Eq}.\quad 8}i}\end{matrix}$

Near the North and South poles the coefficients a, b, d, e and f have anuncertainty in this expansion and this needs to be accounted for byconsidering small angle θ near 0 and π radians. A standard expansion canbe used to accomplish this, as will be appreciated by those skilled inthe art.

In addition to the normal gravity potential of equation 3, there existsa gravity anomaly potential V^((a))(r) that reflects the Earth'sdeviation from a perfect geoid. For the purposes of navigating vehicle10 more accurately and over long trajectories, the gravity anomaly canbe either measured locally or obtained from a map of the anomaly andadded to the normal gravity potential. For computational purposes, theanomaly can be modeled on the assumption that it has a certainmagnitude, a spatial extent and a zero average value. The simplest wayto satisfy these requirements is to assume that the anomaly potentialV^((a))(r) consists of a set of harmonic terms as follows:$\begin{matrix}{{V^{(a)}\left( \overset{->}{r} \right)} = {\sum\limits_{j = 1}^{n_{a}}{h_{aj}\cos\quad{\left( {{\overset{->}{\kappa}}_{aj} \cdot \overset{->}{r}} \right).}}}} & {{Eq}.\quad(10)}\end{matrix}$

Formally, entities 16 move in a hypoeutectic medium having a densityρ=−4πΔV^((a))(r)/G≠0 and could be negative. The choice in equation 10 isused for navigation purposes of the present invention. In fact, in analternative embodiment, a map of the anomaly field can be used instead,if available and as practicable.

We characterize the gravity anomaly by two parameters, an average overspace squared of the gravity anomaly accelerations g_(a) and the scaleof the harmonics in equation 10 of period s_(ga). The wave vectorcomponents are then: $\begin{matrix}{\kappa_{aji} = {\pm \frac{2\pi}{s_{ga}\left( {1 + {2r}} \right)}}} & {{Eq}.\quad 11}\end{matrix}$where r is a random number, amplitudes h_(aj) are normal randomvariables normalized to the given value of g_(a) squared, namely:$\begin{matrix}{g_{a}^{2} = {\frac{\sum\limits_{j = 1}^{n_{a}}{h_{aj}^{2}\kappa_{aj}^{2}}}{2}.}} & {{Eq}.\quad 12}\end{matrix}$

Let us now return to entity 16 released at initial time t_(o) andinitial velocity v_(o) in body frame X into Earth frame X_(e). Entity 16has a velocity v_(e) in Earth frame X_(e) and its position r changeswith time in the Earth's rotating frame as a function of its initialvelocity and the gravitational, Coriolis, centrifugal andgravity-gradient induced forces. Now, in accordance with the invention,initial velocity v_(o) is sufficiently small that entity 16 moves insmall vicinity 32 during the interferometric measurement allowing theapplication of equation 7 to describe the Earth's gravity potentialV^((n))(r). Therefore, the trajectory of entity 16 described by x_(e)(t)evolves in accordance with the following expression:{umlaut over (x)} _(ei) =g _(i) +q _(ik) x _(ek)+2ε_(ikl)Ω_(el) {dotover (x)} _(ek),  Eq. 13where each superscripted dot denotes a time derivative, Ω_(e)=Ω_(e)z,Ω_(e)=7.292115·10⁻⁵ s⁻¹ is the rate of the Earth's rotation, and thetotal acceleration g and gradient tensor q_(ik) consist of the normal,anomaly and centrifugal terms: $\begin{matrix}{{\overset{->}{g} = {{\overset{->}{g}}_{e} + {\sum\limits_{j = 1}^{n_{a}}{h_{aj}{\overset{->}{\kappa}}_{aj}\quad\sin\quad\left( {{\overset{->}{\kappa}}_{aj} \cdot \overset{->}{X}} \right)}} - {{\overset{->}{\Omega}}_{e} \times \left( {{\overset{->}{\Omega}}_{e} \times \overset{->}{X}} \right)}}},} & {{{Eq}.\quad 14}a} \\{{q_{ik} = {{2T_{ik}} + {\sum\limits_{j = 1}^{n_{a}}{h_{aj}\kappa_{aji}\kappa_{ajk}\quad\cos\quad\left( {{\overset{->}{\kappa}}_{aj} \cdot \overset{->}{X}} \right)}} + \left( {{{\overset{->}{\Omega}}_{e}^{2}\delta_{ik}} - {\Omega_{ei}\Omega_{ek}}} \right)}},} & {{{Eq}.\quad 14}b}\end{matrix}$where g_(e) and T_(ik) are given by equations 8a and 8e.

Now, when navigating vehicle 10 over longer periods of time, it isimportant not to use the approximate expression for x_(e)(t), becauseafter numerous steps of navigation, error builds up and violatesinequality 1 in several minutes. For this reason, it is important toobtain precise expression for the trajectory x_(e)(t) of entity 16. TOdo this, we start out by noting that the eigen frequency ω of equation13 obeys the equation:|A(ω)|=0,  Eq. 15aA _(ik)(ω)=q _(ik)+ω²δ_(ik)−2iωε _(ikl)Ω_(el),  Eq. 15bwhich, for the symmetric tensor q_(ik), contains only even powers of ω,i.e., $\begin{matrix}{{{{A(\omega)}} = {a_{o} + {a_{1}\omega^{2}} + {a_{2}\omega^{4}} + \omega^{6}}},} & {{{Eq}.\quad 16}a} \\{{a_{o} = {q}},} & {{{Eq}.\quad 16}b} \\{{a_{1} = {{\frac{1}{2}\left\lbrack {{{Tr}^{2}(q)} - {{Tr}\left( q^{2} \right)}} \right\rbrack} - {4q_{ik}\Omega_{ei}\Omega_{ek}}}},} & {{{Eq}.\quad 16}c} \\{a_{2} = {{{Tr}(q)} - {4{\Omega_{e}^{2}.}}}} & {{{Eq}.\quad 16}d}\end{matrix}$

Since the problem is reduced to the third order equation 16a in ω², onecan obtain an analytic expression for the trajectory. The vector:$\begin{matrix}{\overset{->}{y} = \begin{pmatrix}\overset{->}{x_{e}} \\\overset{.}{\overset{->}{x_{e}}}\end{pmatrix}} & {{Eq}.\quad 17}\end{matrix}$evolves as: $\begin{matrix}{\overset{.}{\overset{->}{y}} = {{\left( {\begin{matrix}0 \\q\end{matrix}\begin{matrix}1 \\{{- 2}\overset{->}{\Omega_{e}} \times}\end{matrix}} \right)y} + {\begin{pmatrix}0 \\\overset{->}{g}\end{pmatrix}.}}} & {{Eq}.\quad 18}\end{matrix}$

The solution of this equation is given by: $\begin{matrix}{{{y(t)} = {{{\Phi(t)}{y(0)}} + {\int_{0}^{t}\quad{{\mathbb{d}t^{\prime}}{\Phi\left( {t - t^{\prime}} \right)}\begin{pmatrix}0 \\\overset{->}{g}\end{pmatrix}}}}},} & {{{Eq}.\quad 19}a} \\{{{\Phi(t)} = {{Y(t)}{Y^{- 1}(0)}}},} & {{{Eq}.\quad 19}b} \\{{{Y(t)} = \left\{ {{{\overset{->}{y}}_{1}(t)},{\ldots\quad{{\overset{->}{y}}_{6}(t)}}} \right\}},} & {{{Eq}.\quad 19}c}\end{matrix}$where y_(i)(t) is an eigen vector of the homogeneous part of equation 18associated with eigen frequency ω_(i). Evidently, $\begin{matrix}{{{{\overset{->}{y}}_{i}(t)} = {\begin{pmatrix}{\overset{->}{x}}_{i} \\{{- {\mathbb{i}}}\quad\omega_{i}{\overset{->}{x}}_{i}}\end{pmatrix}{\mathbb{e}}^{{\mathbb{i}}\quad\omega_{i}t}}},} & {{Eq}.\quad 20}\end{matrix}$where x_(i)(t) is an eigen vector of the homogeneous part of equation13, i.e., the solution of equation A(ω_(i))x_(i)=0. One can group thesix roots of equation 15a into two sub-groups {ω₁,ω₂,ω₃} and{−ω₁,−ω₂,−ω₃}, where $\begin{matrix}{{{\omega_{i} = \sqrt{z_{i} - \frac{a_{2}}{3}}},{z_{1} = {R_{1} + R_{2}}},{{z_{2,3} = {{\frac{{- 1} \pm {i\sqrt{3}}}{2}R_{1}} + {\frac{{- 1} \mp {i\sqrt{3}}}{2}R_{2}}}};}}{{R_{1,2} = \left\lbrack {{- \frac{q}{2}} \pm \sqrt{\frac{q^{2}}{2} + \frac{p^{3}}{27}}} \right\rbrack^{1/3}},{p = {a_{1} - \frac{a_{2}^{2}}{3}}},{q = {\frac{2a_{2}^{3}}{27} - \frac{a_{2}a_{1}}{3} + {a_{o}.}}}}} & {{Eq}.\quad 21}\end{matrix}$

At this point it is convenient to introduce 3×3 matrices x_(±)={{rightarrow over (x)}_(±) ⁽¹⁾,{right arrow over (x)}_(±) ⁽²⁾,{right arrow over(x)}_(±) ⁽³⁾}, where {right arrow over (x)}_(±) ^((i)) is an eigenvector associated with eigen frequency ±ω_(i). Using these matrices, onecan express the 6×6 matrix of equation 19c as: $\begin{matrix}{{{Y(t)} = \begin{pmatrix}{x_{+}{\mathbb{e}}^{{- {\mathbb{i}}}\overset{\sim}{\omega}t}} & {x_{-}{\mathbb{e}}^{{\mathbb{i}}\overset{\sim}{\omega}t}} \\{{- {ix}_{+}}\overset{\sim}{\omega}{\mathbb{e}}^{{- {\mathbb{i}}}\overset{\sim}{\omega}t}} & {{ix}_{-}\overset{\sim}{\omega}{\mathbb{e}}^{{\mathbb{i}}\overset{\sim}{\omega}t}}\end{pmatrix}},{where}} & {{Eq}.\quad 22} \\{{\overset{\sim}{\omega} = \begin{pmatrix}\omega_{1} & \quad & \quad \\\quad & \omega_{2} & \quad \\\quad & \quad & \omega_{3}\end{pmatrix}},} & {{Eq},\quad 23}\end{matrix}$to find that: $\begin{matrix}{{Y^{- 1}(0)} = {\left( \begin{matrix}\left\lbrack {x_{+} + {x_{-}{\overset{\sim}{\omega}}^{- 1}x_{-}^{- 1}x_{+}\overset{\sim}{\omega}}} \right\rbrack^{- 1} & {{ix}_{+}^{- 1}{x_{-}\left\lbrack {{x_{-}\overset{\sim}{\omega}} + {x_{+}\overset{\sim}{\omega}x_{+}^{- 1}x_{-}}} \right\rbrack}^{- 1}} \\{{\overset{\sim}{\omega}}^{- 1}x_{-}^{- 1}\quad x_{+}{\overset{\sim}{\omega}\left\lbrack {x_{+} + {x_{-}{\overset{\sim}{\omega}}^{- 1}x_{-}^{- 1}x_{+}\overset{\sim}{\omega}}} \right\rbrack}^{- 1}} & {- {i\left\lbrack {{x_{-}\overset{\sim}{\omega}} + {x_{+}\overset{\sim}{\omega}x_{+}^{- 1}x_{-}}} \right\rbrack}^{- 1}}\end{matrix}\quad \right).}} & {{Eq}.\quad 24}\end{matrix}$

Representing matrix 19b by 3×3 blocks, ${{\Phi(t)} = \begin{pmatrix}{\Phi_{11}(t)} & {\Phi_{12}(t)} \\{\Phi_{21}(t)} & {\Phi_{22}(t)}\end{pmatrix}},$one obtains the following relevant blocks:Φ₁₁(t)=[x ₊ e ^(−i{tilde over (ω)}t) +x ⁻ e ^(i{tilde over (ω)}t){tildeover (ω)}⁻¹ x ⁻ ⁻¹ x ₊ {tilde over (ω)}][x ₊ +x ⁻{tilde over (ω)}⁻¹ x ⁻⁻¹ x ₊{tilde over (ω)}]⁻¹,  Eq. 25aΦ₁₂(t)=i[x ₊ e ^(−i{tilde over (ω)}t) x ₊ ⁻¹ x ₊ −x ⁻ e^(i{tilde over (ω)}t) ][x ⁻ {tilde over (ω)}+x ₊ {tilde over (ω)}x ₊ ⁻¹x ⁻]⁻¹,  25b

Thus using representation 17 we derive expressions 25 which can beintegrated over t′ in equation 19a to arrive at the following finalresult:{right arrow over (x)} _(e)(t)=x _(x)(t){right arrow over (x)} _(e)(0)+x_(v)(t){right arrow over (v)} _(e)(0)+x _(g)(t){right arrow over(g)},  Eq. 26ax _(x)(t)=[x ₊ e ^(−i{tilde over (ω)}t) +x ⁻ e^(i{tilde over (ω)}t){tilde over (ω)}⁻¹ x ⁻ ⁻¹ x ₊ ω][x ₊ +x_(−{tilde over (ω)}) ⁻¹ x ⁻ ⁻¹ x ₊{tilde over (ω)}]⁻¹,  Eq. 26bx _(v)(t)=i[x ₊ e ^(−i{tilde over (ω)}t) x ₊ ⁻¹ x ⁻ −x ⁻ e^(i{tilde over (ω)}t) ][x ⁻ {tilde over (ω)}+x ₊ {tilde over (ωx)} ₊ ⁻¹x ⁻]⁻¹,  Eq. 26cx _(g)(t)=[x ₊(1−e ^(−i{tilde over (ω)}t)){tilde over (ω)}⁻¹ x ₊ ⁻¹ x ⁻+x ⁻(1−e ^(i{tilde over (ω)}t)){tilde over (ω)}⁻¹ ][x ⁻ {tilde over(ω)}+x ₊ {tilde over (ω)}x ₊ ⁻¹ x ⁻]⁻¹.  Eq. 26d

In the absence of the gravity gradient terms equation 15a becomesdegenerate. In principle, one can get the solution in this case fromequation 26 in the limit:T_(ik)→0.  Eq. 27

A simpler way involves using the Hamiltonian equations of motion insteadof Lagrangian equation 13. In the present case, for the trajectoryx_(e)(t) of entity 16 in Earth frame X_(e) absent the gravity gradientwe obtain: $\begin{matrix}{{{\overset{->}{x}}_{e}(t)} = {{{- \overset{->}{z}} \times \left\{ {{t\left( {{\overset{->}{z} \times {{\overset{->}{v}}_{e}(0)}\cos\quad\Omega_{e}t} + {{{\overset{->}{v}}_{e}(0)}\sin\quad\Omega_{e}t}} \right\}} + {\Omega_{e}^{- 2}\left\lbrack {{\overset{->}{z} \times {\overset{->}{g}\left( {{\cos\quad\Omega_{e}t} + {\Omega_{e}t\quad\sin\quad\Omega_{e}t} - 1} \right)}} + {\overset{->}{g}\left( {{\sin\quad\Omega_{e}t} - {\Omega_{e}t\quad\cos\quad\Omega_{e}t}} \right)}} \right\rbrack}} \right\}} + {\overset{->}{z}\left\lbrack {\overset{->}{z} \cdot \left( {{{\overset{->}{v_{e}}(0)}t} + {\frac{1}{2}\overset{->}{g}t^{2}}} \right)} \right\rbrack}}} & {{Eq}.\quad 28}\end{matrix}$where we assume that x_(e)(0)=0.

Now, to obtain the phases we consider that entity 16 is launched atmoment t_(o) from the point d with velocity v and exposed to opticalpulses 24 at times:t=t _(o) +t ₁ ,t _(o) +t ₁ +T,t _(o) +t ₁+2T  Eq. 29using the n/2-π-π/2 sequence of Raman pulses having the effective wavevector k. The phase of this atom interferometer is thus given by:$\begin{matrix}{{{\phi\left( {\overset{->}{k},\overset{->}{v},\overset{->}{d},t_{o},t_{1}} \right)} = {\overset{->}{k}{\sum\limits_{j = 0}^{2}\quad{\kappa{{\,_{j}\overset{->}{x}}\left( {t_{o} + t_{1} + {jT}} \right)}}}}},{where}} & {{Eq}.\quad 30} \\{{{\kappa_{j} = 1},{- 2},1}{for}\text{}{{j = 0},1,2}} & {{Eq}.\quad 31}\end{matrix}$correspondingly, and x(t) is the atomic trajectory in body frame X.Since after launching entity 16 is decoupled from vehicle 10 andaffected only by the Earth gravitational and inertial forces, it iseasier to work with atom trajectory in the Earth frame X_(e) withconsequent transition to body frame X only at times when Raman pulses 24are applied, i.e., at the times of equation 29. Besides avoiding theconsideration of inertial forces in body frame X, this also allows us toexpress the interferometer phase directly through vehicle 10 positionand orientation.

Assuming that X(t) is the position of the origin of body frame X ofvehicle 10, R(t) is the rotation matrix describing the orientation ofthe axes of body frame X, and x_(e)(t−t_(o)) is the position of entity16 in Earth frame X_(e) with respect to origin of body frame X at thetime of launching, X(t₀), then the trajectory of entity 16 in body frameX is given by:{right arrow over (x)}(t)=R(t)[{right arrow over (x)} _(e)(t−t_(o))+{right arrow over (X)}(t _(o))−{right arrow over (X)}(t)].  Eq. 32

Taking into account the initial condition that entity 16 is launched atmoment to from the point d, i.e., x(t_(o))=d, we find:{right arrow over (x)} _(e)(0)=R ⁻¹(t _(o)){right arrow over (d)}.  Eq.33

The velocity vector v_(e) of entity 16 in Earth frame X_(e) can beobtained now by differentiating equation 32 at t=t_(o) and using thefact that {right arrow over ({dot over (x)})}(t_(o))={right arrow over(v)}_(o), to find that at the time of launching:{right arrow over (v)} _(e)(0)={right arrow over (V)}(t _(o))+R ⁻¹(t_(o))[{right arrow over (v)} _(o)+{right arrow over (Ω)}(t _(o))×{rightarrow over (d)}].  Eq. 34

Using the above expressions and employing an alternative expression forentity 16 trajectory in Earth frame X_(e) as follows:{right arrow over (x)} _(e)(t−t _(o))=R ⁻¹(t _(o)){right arrow over(d)}+[x _(v)(t){right arrow over (v)} _(e)(0)+x _(g)(t){right arrow over(g)}] _({right arrow over (x)}={right arrow over (x)}(t) _(o) _()+R) ⁻¹_((t) _(o) _(){right arrow over (d)}),  Eq. 35which yields the final expression for the interferometer phase:$\begin{matrix}\begin{matrix}{{\phi\left( {\overset{->}{k},\overset{->}{v},\overset{->}{d},t_{o},t_{1}} \right)} = {\overset{->}{k}{\sum\limits_{j = 0}^{2}{\kappa_{j}{R\left( \quad{t_{o}\quad + \quad t_{1} + \quad{jT}} \right)}}}}} \\{\left\{ \begin{matrix}{{{R^{- 1}\left( t_{o} \right)}\overset{->}{d}} + {\overset{->}{X}\left( t_{o} \right)} -} \\{{\overset{->}{X}\left( {t_{o} + t_{1} + {jT}} \right)}{x_{v}\left( {t_{o} + t_{1} + {jT}} \right)}}\end{matrix} \right.} \\{\left\lbrack {{\overset{->}{V}\left( t_{o} \right)} + {{R^{- 1}\left( t_{o} \right)}\left( {\overset{->}{v} + {{\overset{->}{\Omega}\left( t_{o} \right)} \times \overset{->}{d}}} \right)}} \right\rbrack +} \\\left. {{x_{g}\left( {t_{o} + t_{1} + {jT}} \right)}\overset{->}{g}} \right\}_{\overset{\rightarrow}{X} = {{\overset{\rightarrow}{X}{(t_{o})}} + {{R^{- 1}{(t_{o})}}\overset{\rightarrow}{d}}}}\end{matrix} & {{Eq}.\quad 36}\end{matrix}$

Performance Examples

The method of invention can be used to restore the rotation matrix forany given body trajectory and rotation under the influence of noise.Since we can restore body orientation independently, as described above,we first examine the performance of rotation matrix R(t) restorationunder a relative inaccuracy defined as: $\begin{matrix}{{{\Delta\quad{R(t)}} \equiv \sqrt{\frac{{Tr}\left\{ {\left\lbrack {{R(t)} - {R_{e}(t)}} \right\rbrack^{T}\left\lbrack {{R(t)} - {R_{e}(t)}} \right\rbrack} \right\}}{3}}},} & {{Eq}.\quad 37}\end{matrix}$where R(t) is the exact rotation matrix. The recurrent relation causesthe roundoff errors for rotation matrix R(t) to increase slowly in timewhen one performs the calculations with quadrupole precision. Examplesof the dependencies ΔR(t) are shown in FIG. 8. They were obtained for atime delay T=5 ms between optical pulses, minimal number ofinterpolation points n_(i)=3, and body acceleration on the order of g(scale parameter s_(c)=1). Using exact body trajectory and rotationmatrices we calculated the phases of the basic and additional atominterferometers. Their difference was used in the analogue of equation17 (see above section entitled “Operation including body rotation in aninertial frame with a homogeneous gravity field”) valid for a finiterotation matrix to restore R(t). In addition, we inserted into the inputphases a random term δφ_(r), chosen homogeneously from the interval:$\begin{matrix}{{{\delta\phi}_{r}} \leq \frac{\delta\phi}{2}} & {{Eq}.\quad 38}\end{matrix}$

From the results, we see that the roundoff error (for δφ=0) does notexceed:ΔR(t)≦1.9×10⁻²¹,  Eq. 39while the rather moderate level in phase inaccuracy δφ=10⁻³ leads to anorientation inaccuracy of:ΔR(t)≦3.9×10⁻⁸=2.2 μdeg.  Eq. 40

To restore body position X(t) we varied time delay T between pulses from1 ms to 100 ms with a step of 1 ms. For each value of T we varied thenumber of points n_(i) from 3 to 20. For any given T and n_(i) werestored body position and rotation matrix in time until the requirementof ΔX(t)≦5 m was violated or up to a maximum time of 1.5 hours. Wedetermined an optimum number n_(iopt)(T) and maximum value of timet_(max)(T).

We considered two types of body motion; oscillatory motion and pulsedmotion. Examples of oscillatory trajectories as restored are shown inFIG. 10. We introduced a scale parameter sc such as typical bodyacceleration is on the order of s_(c)g. Calculations have been performedfor scale factors s_(c)=1, 0.5, 0.25 and 0.1. For the last scale factorvalue of 0.1, the program was run for five different sets ofacceleration and rotation matrices. Dependencies n_(iopt)(T) andt_(max)(T) are shown in FIGS. 9A-E. We see that restoration of bodytrajectory occurs for time delay T between pulses and number ofinterpolation points n_(i) on the order of:T≈6-10 ms, n_(i)≈4-17.  Eq. 41

Example of exact body trajectory and that restored with the method ofinvention is shown in FIG. 10.

In another example, it was assumed that the body was accelerated androtated only by a pulse applied at the start. For the pulse ofacceleration we chose the Lorentz shape: $\begin{matrix}{{{a_{si}(t)} = {a_{0i}\frac{\tau_{si}^{2}}{t^{2} + \tau_{si}^{2}}}},{\tau_{si} \in \left\{ {0,{600s}} \right\}},} & {{Eq}.\quad 42}\end{matrix}$which corresponds to the smooth part of the body trajectory:$\begin{matrix}{X_{si} = {a_{0i}{{\tau_{si}\left\lbrack {t - {\tau\quad{\ln\left( \frac{t + \tau}{\tau} \right)}}} \right\rbrack}.}}} & {{Eq}.\quad 43}\end{matrix}$

For a pulse in the Euler angle α we chose: $\begin{matrix}{{{a(t)} = {\alpha_{m}\frac{16t^{2}\tau_{\alpha}^{2}}{\left( {t^{2} + \tau_{\alpha}^{2}} \right)^{2}}}},{\tau_{\alpha} \in \left\{ {0,{600s}} \right\}},{\tau_{m} \in \left\{ {0,{2\pi}} \right\}},} & {{Eq}.\quad 44}\end{matrix}$and the same pulses for angles β and γ, except that the maximum value ofβ did not exceed π (β_(m)∈{0,π}).

As in the case of oscillatory motion, numerical calculation showsreliable restoration of body trajectory during 1 hour for scaling factors_(c)=0.1. The relationship between the optimum number of interpolationpoints n_(iopt)(T) and maximum time t_(max)(T) after which the error inbody position surpassed 5 m is shown in FIGS. 11A-E. The trajectoriesare found in FIGS. 12A-E.

One concludes that for the pulsed trajectory the time delay T betweenRaman pulses and the number of interpolation points can be on the orderof:T≈150-200 ms, n _(i≈)3-20.  Eq. 45

For the case of a body moving in the Earth frame X_(e), simulations ofthe navigation process have been performed using equations 26 and 36with basic and additional interferometers. Typical examples ofsimulations for five different trajectories are shown in FIGS. 13 and 14for the case when the angle of body rotation φ_(i)(t) don't exceed 10⁻⁵radians and the error in the interferometer phase measurement in on theorder of 10⁻⁴. Under these assumptions, FIG. 13 shows the dependence ofthe maximum time navigation on the time delay between Raman pulses. FIG.14 shows the build up of error in body position, body velocity andgravity acceleration during the navigation process.

Based on the above embodiments and specific examples, it will be clearto a person skilled in the art that the method and apparatus ofinvention admit of many variations. Moreover, the method can bepracticed in various types of known frames in addition to thosedescribed above. Therefore, the scope of invention should be judgedbased on the appended claims and their legal equivalents.

1. A method for determining coordinates of a body: a) providing atominterferometers in a body frame X; b) releasing interfering entitiesinto a known frame X′ decoupled from said body frame X; c) applying anoptical pulse sequence to said interfering entities to affectmatter-wave phases of said interfering entities as a function of saidcoordinates; d) determining said coordinates from phases of said atominterferometers.
 2. The method of claim 1, wherein said optical pulsesequence comprises a π/2-π-π/2 sequence.
 3. The method of claim 1,wherein said optical pulse sequence comprises a Raman pulse sequence. 4.The method of claim 1, wherein said atom interferometers are triggeredat regular time intervals.
 5. The method of claim 1, wherein saidinterfering entities are selected from the group consisting of atoms,ions and molecules.
 6. The method of claim 5, wherein said interferingentities comprise atoms released in the form of a gas cloud.
 7. Themethod of claim 1, wherein said atom interferometers comprise basic atominterferometers for operating on interfering entities released at aninitial time t_(o) and a zero initial velocity v_(o)=0 in said bodyframe X.
 8. The method of claim 7, wherein said atom interferometerscomprise additional atom interferometers for operating on interferingentities released at said initial time t_(o) and at a non-zero initialvelocity v_(o)≠0 in said body frame X.
 9. The method of claim 8, whereinbody rotation matrices R are determined from phase differences betweensaid basic atom interferometers and between said additional atominterferometers, and from rotation matrices R restored for precedingmeasurement times.
 10. The method of claim 7, wherein body coordinatesare determined from the phases of said basic atom interferometers,restored rotation matrices R, body coordinates restored for precedingmeasurement times and body velocities at the times of releasing saidinterfering entities.
 11. The method of claim 1, wherein a velocity ofsaid body at the time of releasing said interfering entities forsubsequent atom interferometeric measurements is obtained byinterpolation from restored body positions and said optical pulsesequence is applied with a time delay.
 12. The method of claim 1,wherein said known frame X′ is the Earth frame X_(e).
 13. The method ofclaim 12, wherein an initial velocity of said interfering entities inEarth frame X_(e) is sufficiently small to allow the Earth's normalgravity potential V(r) to be expressed by the following expression:V ^((n))({right arrow over (r)})=V _(o) −{right arrow over (x)}·{rightarrow over (g)} _(e) −T _(ik) x _(i) x _(k) where g_(e) is gravityacceleration and T_(ik) is gravity gradient tensor.
 14. The method ofclaim 12, wherein Earth's gravity potential is composed of a normalgravity potential V^((n))(r) and an anomalous gravity potentialV^((a))(r).
 15. An apparatus for determining coordinates of a body, saidapparatus comprising: a) atom interferometers in a body frame X; b)interfering entities released into a known frame X′ decoupled from saidbody frame X; c) a source for applying an optical pulse sequence to saidinterfering entities to affect matter-wave phases of said interferingentities as a function of said coordinates; d) a unit for determiningsaid coordinates from phases of said atom interferometers.
 16. Theapparatus of claim 15, wherein said atom interferometers comprise basicatom interferometers for operating on said interfering entities releasedat an initial time t_(o) and a zero initial velocity v_(o)=0 in saidbody frame.
 17. The apparatus of claim 15, wherein said atominterferometers comprise additional atom interferometers for operatingon said interfering entities released at an initial time t_(o) and anon-zero initial velocity v_(o)≠0 in said body frame.
 18. The apparatusof claim 15, wherein said body is a vehicle.
 19. The atom interferometerof claim 15, wherein said interfering entities are selected from thegroup consisting of atoms, ions and molecules.
 20. The atominterferometer of claim 15, wherein said known frame X′ is the Earthframe X_(e).